TY - JOUR
T1 - Analysis of the mechanism by which melatonin inhibits human eosinophil peroxidase
AU - Lu, T.
AU - Galijasevic, S.
AU - Abdulhamid, I.
AU - Abu-Soud, H. M.
PY - 2008/7
Y1 - 2008/7
N2 - Background and purpose: Eosinophil peroxidase (EPO) catalyses the formation of oxidants implicated in the pathogenesis of various respiratory diseases including allergy and asthma. Mechanisms for inhibiting EPO, once released, are poorly understood. The aim of this work is to determine the mechanisms by which melatonin, a hormone produced in the brain by the pineal gland, inhibits the catalytic activity of EPO. Experimental approach: We utilized H 2O 2-selective electrode and direct rapid kinetic measurements to determine the pathways by which melatonin inhibits human EPO. Key results: In the presence of plasma levels of bromide (Br -), melatonin inactivates EPO at two different points in the classic peroxidase cycle. First, it binds to EPO and forms an inactive complex, melatonin-EPO-Br, which restricts access of H 2O 2 to the catalytic site of the oxidation enzyme. Second, melatonin competes with Br - and switches the reaction from a two electron (2e -) to a one electron (1e -) pathway allowing the enzyme to function with catalase-like activity. Melatonin is a bulky molecule and binds to the entrance of the EPO haem pocket (regulatory sites). Furthermore, Br - seems to enhance the affinity of this binding. In the absence of Br -, melatonin accelerated formation of EPO Compound II and its decay by serving as a 1e - substrate for EPO Compounds I and II. Conclusions and implications: The interplay between EPO and melatonin may have a broader implication in the function of several biological systems. This dual regulation by melatonin is unique and represents a new mechanism for melatonin to control EPO and its downstream inflammatory pathways.
AB - Background and purpose: Eosinophil peroxidase (EPO) catalyses the formation of oxidants implicated in the pathogenesis of various respiratory diseases including allergy and asthma. Mechanisms for inhibiting EPO, once released, are poorly understood. The aim of this work is to determine the mechanisms by which melatonin, a hormone produced in the brain by the pineal gland, inhibits the catalytic activity of EPO. Experimental approach: We utilized H 2O 2-selective electrode and direct rapid kinetic measurements to determine the pathways by which melatonin inhibits human EPO. Key results: In the presence of plasma levels of bromide (Br -), melatonin inactivates EPO at two different points in the classic peroxidase cycle. First, it binds to EPO and forms an inactive complex, melatonin-EPO-Br, which restricts access of H 2O 2 to the catalytic site of the oxidation enzyme. Second, melatonin competes with Br - and switches the reaction from a two electron (2e -) to a one electron (1e -) pathway allowing the enzyme to function with catalase-like activity. Melatonin is a bulky molecule and binds to the entrance of the EPO haem pocket (regulatory sites). Furthermore, Br - seems to enhance the affinity of this binding. In the absence of Br -, melatonin accelerated formation of EPO Compound II and its decay by serving as a 1e - substrate for EPO Compounds I and II. Conclusions and implications: The interplay between EPO and melatonin may have a broader implication in the function of several biological systems. This dual regulation by melatonin is unique and represents a new mechanism for melatonin to control EPO and its downstream inflammatory pathways.
KW - Allergy
KW - Asthma
KW - Halides
KW - Inflammation
KW - Mammalian peroxidases
KW - Stopped flow
UR - http://www.scopus.com/inward/record.url?scp=47249119192&partnerID=8YFLogxK
U2 - 10.1038/bjp.2008.173
DO - 10.1038/bjp.2008.173
M3 - Article
C2 - 18516076
AN - SCOPUS:47249119192
VL - 154
SP - 1308
EP - 1317
JO - British Journal of Pharmacology
JF - British Journal of Pharmacology
SN - 0007-1188
IS - 6
ER -